Think about performance. When developing a brief, it is tempting to refer to explicit design solutionsfor example, saying that the entrance hall should have a chic travertine floor, or that the building should be equipped with a powerful air conditioning system. Such specifications are called prescriptive specifications: they prescribe specific solutions in terms of systems, materials, dimensions or products. It is a natural thing to do, but such specifications interfere with the design process and they limit the design teams ability to come up with alternative, perhaps better solutions.So, ideally the brief should not focus on the design itself, but on the desired outcomes, using so-called performance specifications or output specifications. To use the earlier example of the air conditioning system again: performance specifications do not say anything about the air conditioning system itself, but only about the desired thermal comfort in terms of temperature levels. The good thing about such performance specifications is that they focus on user needs while leaving the design team with the freedom to come up with an effective solution, which may not necessarily be air conditioning. The disadvantage of performance specifications is that they can be complex and abstract, giving the client little certainty or control over the buildings design. When clients have no direct involvement in the design process (as in Design & Build projects), they may feel insecure about what they will get. In such cases, the use of reference solutions may help. This allows the client to spell out the design solutions they have in mind, while giving the design team the freedom to propose other solutions of equal quality.Some clients have good reason to be very precise about the design solutions they want. Retail chains for example tend have very specific design briefs because they want all their outlets to look exactly the same. Also, professional clients may have very prescriptive specifications that are based on their wide experience with other projects. In general, however, the aim of briefing should be to explain what the design should do for the client, and not dictate the design itself. Recommendations-When formulating requirements, focus on function, not on form.-Formulate test methods for performance specifications. How can the requested performance be measured?-Take the design teams expertise into account. A highly knowledgeable design team will need a less specific brief than an inexperienced one.-Do not be dogmatic in the use of performance specifications. Referring to a solution can be helpful for the design team to understand what is expected from them.-When using performance specifications in integrated contracts (e.g. Design and Build contracts), connect these to a procedure for the testing and acceptance of design proposals.